3 (or possibly 4 - I didn't ask) of the speakers I invited started companies, with zero funding or with a bit of F&F, that have revenues from nearly-$2 mil/yr to more than $2 mil/yr.
Maybe you should write them to tell them that it's not possible without $5,000 of funding for a summer.
On the balance, if you can't manage to figure out ways to save $5k for a summer yourself, you should seriously question whether you have the ability to run a business.
If you can't figure out how to pay for 250 euros a month - which you could earn each week as a dishwasher in Vienna, so it's not as if it's some vast sum - then you are similarly ill-equipped.
If you can't bear to give up one week of your time in order to spend the other 3 weeks on your huge future business, ditto.
By the way: I wrote an ebook to self-fund our work on Freckle and it earned us over $40k. It was sooooooo haaaaaaard. But even then, it was cream - not necessary. We could have kept working on it after hours for free, as we had been doing. It would have taken a bit longer, but so what?